Residency & Working (Hamburg)

I am an American moving to Hamburg/Buchholtz area in May. My partner is German but we are not married. I want to "get legal" as an American over 45 who wants to work as a contractor and start some online based businesses.

My understanding is that it is VERY complicated to get just what I want as far as permissions and residency for working. I have a German company and an independent business person who have written letters of intent to use me as a contractor for their projects. And I already have those jobs lined up in the next few months as a continuation of work I have already been performing for them for several years.

But I understand that as a "freelancer" with special talents that it depends on the particular official as to how "special" and unique they assess my skillset.

And I have been given the understanding that being over 45 I must show a retirement pension fund in place, which I do not have. I want to establish something equivalent through the income of contracts and several online businesses.

The regulations I have seen do not specify what exactly satisfies the "retirement fund" requirement to make officialdom happy.

From research I have done so far it seems that there are agencies that offer this kind of "legal" help in walking me through the German maze with the best possible chance of success.

Is this a correct assumption? That I need experienced professionals who know this process and who regularly work with foreign nationals to get a favorable immigration and work status secured?